Overhaul (#4)

**README**
- Overhaul; changed docs to be better aligned to the new `backup.sh`.
- Add example `docker-compose`.

**Dockerfile**
- Install `zip`.
- Remove installation of `sqlite`.
- Remove unnecessary variables.

**backup.sh**
- Overhaul; now zips all required and recommended files and directories stated at [vaultwarden docs](https://github.com/dani-garcia/vaultwarden/wiki/Backing-up-your-vault).
- Removed deleting old backups; will be added later on in a separate script.

**entrypoint.sh**
- Removed creating folders.

Dockerfile

@@ -4,18 +4,12 @@ FROM ${ARCH}alpine:latest
 RUN addgroup -S app && adduser -S -G app app
 
 RUN apk add --no-cache \
-    sqlite \
     busybox-suid \
     su-exec \
+    zip \
     tzdata
 
-ENV DB_FILE /data/db.sqlite3
-ENV BACKUP_FILE /data/db_backup/backup.sqlite3
-#ENV ATTACHMENT_BACKUP_FILE=/data/attachments_backup/attachments
-ENV ATTACHMENT_DIR=/data/attachments
-ENV BACKUP_FILE_PERMISSIONS 700
 ENV CRON_TIME "0 5 * * *"
-ENV TIMESTAMP false
 ENV UID 100
 ENV GID 100
 ENV CRONFILE /etc/crontabs/root
@@ -29,6 +23,5 @@ RUN mkdir /app/log/ \
     && chown -R app:app /app/ \
     && chmod -R 777 /app/ \
     && chmod +x /usr/local/bin/entrypoint.sh 
-#    && echo "\$CRON_TIME \$BACKUP_CMD >> \$LOGFILE 2>&1" | crontab -
 
 ENTRYPOINT ["entrypoint.sh"]